Fig. 2: Influence of sample preparation techniques on piperacillin concentrations.

Comparison of the piperacillin concentrations of the untreated and treated samples for the individual sample preparation steps [i.e., freezing (a), filtration (b), centrifugation (c), and filtration combined with centrifugation (d)]. The concentrations of the treated samples were determined through a PLS regression model based on the untreated samples. The correlation between these concentration values indicates the influence of individual sample preparation steps. The factor (see Table 1) was calculated by minimizing the RMSEP of the concentrations of the respective treated and untreated samples [see Eq. (1)], resulting in an almost perfect linear relationship (identity function, dashed line). Filtration and centrifugation have a small effect on the concentration change of piperacillin, while freezing shows the largest effect. The boxplot shows the predicted concentrations resulting from a 50-fold cross-validation of n = 3 replicate measurements. In addition, all obtained measurements are shown, jittered for better visualization.